Might have been this one: https://www.wellbeingintlstudiesrepository.org/cgi/viewcontent.cgi?article=1051&context=acwp_asie
There was another by the same group I think where they reverse the behaviour modifications by giving the fishies a shot of opiates, and then they stop hiding and rubbing their faces.
edit: I should add why I found this so morally concerning; it hints very strongly at an experience of pain, not just nociception. They don't just run from a bad stimulus, they nurse the site and become more cautious. Something which is hard to explain except if you suppose that like us they have some persistent emotional state which affects how they judge appropriate behaviours. Additionally rubbing, which is commonly observed in humans, indicates an attempt to sooth a spot after harm.
We were ovo pesco at the time and it just made me realise that if fish, which diverged from land animals how many millions of years ago, likely shared so much in the experience of pain including nursing behaviours and becoming more cautious then either these behaviours are highly convergent and frequently occuring or they are very old. Both hinting that consciousness might be extremely similar between living beings.
In other words, Nirvana lied and fish probably do have feelings and that is a horrifying realisation considering how they're treated. If fish, what new discovery would I wait for before pleading "how could I have known?" why not just take a proper and coherent stance against suffering and draw the line at the presence of a nervous system since it's very doable.
I've recently been making sandwich sausage with seitan, tvp, and bessan (texture and balancing out aminos) plus herbs and spices maybe sundried Ts.
Shit is easy, affordable, and lasts all week.